JP5090318B2 - Receive module - Google Patents

Description

  The present invention relates to a receiving module for optical communication, and more particularly to a small receiving module capable of receiving optical signals having different signal speeds.

  In recent years, large-capacity optical communication systems have been introduced into various networks with the development of technologies such as broadbanding of the Internet and high definition of moving images. In such an optical communication system, the signal speed of the optical signal differs depending on the application and the applied network, and the signal speed tends to be further diversified in the future.

  Therefore, in a network in which optical signals having different signal speeds are mixed, a multi-rate optical reception technology capable of receiving optical signals having different signal speeds by one module is expected to be used in the future in an optical communication system and its network. It is expected as an important fundamental technology for realizing

Conventionally, as a multi-rate optical reception technique, a configuration having a signal speed switching terminal has been used so that a desired operation according to the signal speed of a received optical signal can be performed (for example, Patent Document 1 and Non-Patent Document below). Reference 1).
FIG. 6 is a schematic diagram showing a conventional receiving module.
As shown in FIG. 6, in the conventional receiving module, a constant voltage source 64 is connected to the cathode side of the photodiode 61 via surge protection capacitors 62 and 67 and an overcurrent prevention resistor 63, and to the anode side. An input terminal of the transimpedance amplifier 65 is connected, a signal speed switching terminal 66 is connected to the transimpedance amplifier 65, and an output terminal is output from the transimpedance amplifier 65.

  In general, a product of gain and band (= GB product) is often used as a performance index of a receiver. A system with low signal speed requires high reception sensitivity, and a system with high signal speed requires a wide reception band. That is, in the conventional multi-rate optical reception technology, when the signal speed is low, the feedback resistance is increased by increasing the feedback resistance when the signal speed switching signal is input to the transimpedance amplifier 65, and when the signal speed is high, the feedback resistance is increased. A circuit that widens the reception band by reducing the frequency is introduced in the feedback resistance portion of the transimpedance amplifier 65. As a result, the conventional multi-rate optical reception technology enables appropriate reception according to the signal speed.

JP 2004-274173 A Keiji Tanaka and nine others, “Technological Development of Multi-rate Compact Pluggable Optical Link”, SEI Technical Review, No. 172, January 2008, p. 133-138

  In the optical access system, standardization of a 10GE-PON (Gigabit Ethernet (registered trademark) -Passive Optical Network) system based on a signal speed of 10 Gbps is being advanced in accordance with the recent trend toward higher speeds. In this standardization, application in a form mixed with an existing GE-PON system has also been proposed. In this form, a multi-rate capable of receiving both low-speed and high-speed optical signals in the receiving module on the base station side. An optical reception function is required.

  A receiving module used in such a 1 Gbps / 10 Gbps mixed PON system is strongly required not only to perform a multi-rate compatible receiving operation, but also to be low in cost and have high operability from a control circuit. . However, the conventional multi-rate reception module that requires the control signal described above complicates the configuration and control method of the module, which increases the cost of the multi-rate reception module and the entire transmission apparatus using the multi-rate reception module. It is a factor of.

  From the above, the present invention solves the above-described problems in the prior art, and in the case of performing optimal reception according to the reception speed, the signal speed switching terminal that was conventionally required is unnecessary, It is an object of the present invention to provide a receiving module that does not require a complicated module configuration or complicated control, and can support multirate at a low cost.

A receiving module according to a first invention for solving the above-mentioned problems is as follows.
A light receiving element that converts the received optical signal into an electrical signal;
In a receiving module comprising an electrical amplifying element that amplifies the converted electrical signal,
The electrical amplifying element, to accommodate both the two optical signals different Do that the signal speed in one of the electric amplifier element, the signal amplification characteristic having a frequency band of the gain and the optical signal suitable for signal speed of the optical signal Bei to give a frequency characteristic obtained by adding a,
The optical signal is a multi-rate signal that is modulated by the NRZ method and transmitted at a signal speed of either 1.25 Gbps or 10.3125 Gbps for each optical signal;
The gain suitable for the signal speed of each optical signal is higher for the signal speed of 1.25 Gbps than the gain for the signal speed of 10.3125 Gbps,
The signal amplification characteristic having the frequency band of each optical signal has a flat gain from at least a frequency of 3 GHz to 8 GHz for the signal speed of 10.3125 Gbps, and at least a frequency for the signal speed of 1.25 Gbps. The gain is flat up to a frequency required to pass a signal of 1.25 Gbps modulated by NRZ system from 0 GHz, and the frequency is 1.5 GHz or less .

A receiving module according to a second invention that solves the above problem is the receiving module according to the first invention,
The electric amplifying element is configured by arranging at least two transimpedance amplifiers having different gains and frequency bands in parallel or in combination of parallel and series.

A receiving module according to a third invention for solving the above problem is the receiving module according to the first invention,
The electrical amplifying element includes at least one transimpedance amplifier, and a feedback circuit in the transimpedance amplifier is configured by combining one or more passive elements and active elements.

A receiving module according to a fourth invention for solving the above-mentioned problems is the receiving module according to the third invention,
A circuit configuration in which at least two of the electric amplifying elements are arranged in parallel or a combination of parallel and series is formed on one monolithic integrated circuit.

  According to the receiving module of the present invention, a frequency characteristic obtained by adding a signal amplification characteristic having a gain suitable for the signal speed of each optical signal and a frequency band of each optical signal to at least two optical signals having different signal speeds. It is possible to cope with a plurality of signal speeds without inputting a control signal for switching the gain of the electric amplification element and its frequency band according to the signal speed. Simplification of the configuration can be achieved. Further, a control circuit related to the control signal can be omitted, so that the cost can be reduced and the operation can be stabilized.

  In the electrical amplifying element, at least two transimpedance amplifiers having different gains and their frequency bands are arranged in parallel or a combination of parallel and series, so that the sum of the characteristics of each transimpedance amplifier is obtained. Since it is possible to realize a frequency characteristic obtained by adding a gain suitable for each corresponding signal speed and a signal amplification characteristic having the frequency band, it is possible to obtain a stable characteristic with a simple configuration and good design.

  The electrical amplifying element is composed of at least one transimpedance amplifier, and a feedback circuit in the transimpedance amplifier is configured by combining one or more passive elements and active elements, and the feedback rate is changed according to the signal speed. By doing so, it becomes possible to configure a transimpedance amplifier having a gain suitable for each signal speed and its frequency characteristics, increasing the degree of freedom of design, and designing that meets various characteristics requirements.

  In addition, since a circuit configuration in which at least two electric amplifying elements are arranged in parallel or a combination of parallel and serial is formed on one monolithic integrated circuit, it corresponds to the sum of the characteristics of at least two electric amplifying elements. Therefore, it is possible to realize a frequency characteristic obtained by adding a gain suitable for each signal speed and a signal amplification characteristic having the frequency band, and to achieve a reduction in size and power consumption by monolithicization.

  Embodiments of a receiving module according to the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a receiving module according to the first embodiment of the present invention.
As shown in FIG. 1, the receiving module according to the present invention includes a photodiode 11, capacitors 12 and 17, a fixed resistor 13, a constant voltage source 14, and transimpedance amplifiers 15 and 16.

  Capacitors 12 and 17 for preventing surges are connected in parallel with the photodiode 11 on the cathode side of the photodiode 11, that is, on the bias circuit side. A voltage source 14 is connected. Here, as the capacitors 12 and 17, capacitors of about 100 pF and 0.1 μF are used, respectively, and as the fixed resistor 13, resistors having a resistance value of about 2 kΩ are used.

  As a result of various studies, the inventor of the present application, when receiving two signals having different signal speeds, transimpedance amplifiers 15 and 16 having optimized gains and frequency bands in accordance with the respective signal speeds, By connecting in parallel to the anode side of 11, it was found that optimum sensitivity can be obtained even for different received signals, and the present invention has been achieved. The specific design of the transimpedance amplifiers 15 and 16 can be designed by using a general-purpose tool such as a general-purpose circuit simulator. In addition, although a configuration in which two signals having different signal speeds are received will be described here, a configuration in which three or more signals having different signal speeds are received may be employed.

  FIG. 2 is a diagram illustrating the frequency dependence of the reception gain of the reception module according to the first embodiment of the present invention. Note that FIG. 2 shows the frequency characteristics of an actually manufactured reception module, where the horizontal axis represents frequency and the vertical axis represents gain. Further, in the prototype receiving module, the transimpedance amplifier is optimized at each frequency so that two types of signals having different signal frequencies of 1.25 Gbps and 10.3 Gbps can be received.

  As shown in FIG. 2, in the receiving module according to the present embodiment, the gain is as large as 70 dBΩ up to about 1.5 GHz, but the gain decreases drastically when the frequency becomes higher than 1.5 GHz, and from 3 GHz to about 8 GHz. A frequency characteristic is obtained in which the gain is almost constant at about 65 dBΩ and the gain decreases with increasing frequency when the frequency exceeds 8 GHz.

  In order to confirm whether or not the receiving module having such frequency characteristics has an optimum receiving sensitivity characteristic, a bit error rate measurement was performed using a light source modulated at 1.25 Gbps and 10.3 Gbps. The modulation method of the light source is the NRZ method, the signal format is a pseudo-random signal, the number of stages is 7 for 1.25 Gbps, 31 is the stage for 10.3 Gbps, and the mark rate is 50%.

  FIG. 3 is a diagram illustrating the dependence of the bit error rate on the reception power of the reception module according to the first embodiment of the present invention. FIG. 3 shows the measurement result of the bit error rate at each signal speed, with the horizontal axis representing the average received power and the vertical axis representing the bit error rate.

As shown in FIG. 3, in the receiving module according to the present embodiment, the bit error rate increases when the received power is low, but the bit error rate decreases as the received power increases. The minimum receiving sensitivity (receiving power at 10 ⁻¹² ) at 1.25 Gbps was −30 dBm, while the minimum receiving sensitivity at 10.3 Gbps was −20.5 dBm.

  In this prototype receiving module, a high gain can be set in a relatively low frequency band of about 1.5 GHz, so that when the signal speed is low (for example, 1.25 Gbps), high receiving sensitivity is obtained. . On the other hand, although the gain is relatively small up to about 3 to 8G, a wide band is obtained, so that a relatively high reception sensitivity is obtained even when the signal speed is high (for example, 10.3 Gbps).

  As described above, according to the receiving module according to the present embodiment, two transimpedances 15 and 16 having different gains and frequency bands are connected in parallel to obtain frequency characteristics suitable for two signal speeds. Therefore, it is possible to realize a multi-rate compatible receiving module that does not require switching of the feedback resistance of the transimpedance amplifier by a signal speed switching signal that has been conventionally required. Here, a configuration using two transimpedances 15 and 16 having different gains and frequency bands will be described, but a configuration using three or more transimpedances is also possible.

In the example described above, two different single-ended transimpedance amplifier receiving modules are connected in parallel, but a differential transimpedance amplifier may be connected.
FIG. 4 is a schematic diagram showing a differential output form of the receiving module according to the first embodiment of the present invention.
As shown in FIG. 4, in the differential output form of the receiving module according to the present embodiment, the positive phase output of the differential transimpedance amplifier 45 having a frequency band wider than the received signal speed is optimal for a low signal speed. The differential transimpedance amplifier 46 is connected, the differential transimpedance amplifier 47 optimized for a high-speed signal is connected to the negative phase output, and the positive and negative phase output terminals of the transimpedance amplifiers 46 and 47 are connected. Are connected to each other.

  According to the differential output form of the receiving module according to the present embodiment, by using the differential transimpedance amplifiers 45 to 47, the noise tolerance of the receiving module is increased and the reception sensitivity can be further increased. Have.

  Here, a transimpedance amplifier has been described as an example of an electric signal amplifier, but the present invention is not limited to this, and various amplifiers such as a high impedance amplifier and a distributed amplifier may be designed. It goes without saying that a desired amplification frequency band can be set by various combinations of series connection and parallel connection instead of simple parallel connection. It is also possible to form a circuit configuration in which at least two electric amplifying elements are arranged in parallel or in a combination of parallel and series on one monolithic integrated circuit.

  In addition, although details are not specified in particular, a reset signal terminal required for operation switching such as gain switching is provided when receiving burst optical signals having the same signal speed and different light intensity in optical packet communication or PON. It should also be noted that the structure provided in the receiving module according to the present embodiment is also useful in practice.

FIG. 5 is a schematic diagram showing a form in which the gain of the receiving module according to the second embodiment of the present invention changes according to the signal speed.
As shown in FIG. 5, the receiving module according to the present embodiment is provided with a low-pass filter in the feedback resistor portion of the transimpedance amplifier 51 connected to the anode side of the photodiode 11. In this transimpedance amplifier 51, a resistor 53 is connected from the output terminal side of the operational amplifier 52, and a parallel circuit of a resistor 54 and a capacitor 55 is connected in series to the resistor 53 and fed back to the input terminal side of the operational amplifier 52. It is the composition which is.

  Here, for example, when the resistance 53 is 400 kΩ, the resistance 54 is 800 Ω, and the capacitance 55 is 0.2 pF, a transimpedance gain of about 58 dBΩ is obtained at 1 GHz, and about 53 dBΩ is obtained at 10 GHz. Thus, by using a low-pass filter instead of the feedback resistor of the transimpedance amplifier 51, the gain can be set high for a low-speed signal, and the gain is set small for a high-speed signal. Therefore, it is possible to perform an appropriate reception setting according to the signal speed.

  Note that the configuration of the low-pass filter described above is an example, and is not limited to this configuration. By appropriately combining passive elements such as various resistors and capacitors and active elements such as transistors, a low-pass filter is provided. It is possible to configure a filter. Various element parameters can be designed by a general-purpose circuit simulator.

  The configuration of the receiving module according to the present invention described above is not limited to the configuration described above, and various modifications can be made without departing from the scope of the present invention and the spirit of the present invention. It is obvious to those who have common knowledge in the technical field, and the scope of the present invention should not be limited to the above-described embodiments, but is defined within the scope of the claims and equivalents thereof. It should be.

  As described above, the receiving module according to the present invention includes a light receiving element that converts a received optical signal into an electric signal, and an electric amplifying element that amplifies the converted electric signal. Has a frequency characteristic obtained by adding a gain suitable for the signal speed of each optical signal and a signal amplification characteristic having a frequency band of each optical signal to at least two optical signals having different signal speeds. Accordingly, it is possible to cope with a plurality of signal speeds without inputting a control signal for switching the gain of the electric amplifying element and its frequency band, and the configuration of the module can be simplified. Further, a control circuit related to the control signal can be omitted, so that the cost can be reduced and the operation can be stabilized.

  Therefore, according to the present invention, when performing optimal reception according to the reception speed, a signal speed switching terminal, which is conventionally required, is unnecessary, a complicated module configuration and complicated control are not required, and low cost multirate Can be realized.

It is the schematic diagram which showed the receiving module which concerns on 1st Example of this invention. It is the figure which showed the frequency dependence of the reception gain of the receiving module which concerns on 1st Example of this invention. It is the figure which showed the received power dependence of the bit error rate of the receiving module which concerns on 1st Example of this invention. It is the schematic diagram which showed the differential output form of the receiving module which concerns on 1st Example of this invention. It is the schematic diagram which showed the form from which the gain of the receiving module which concerns on 2nd Example of this invention changes according to a signal speed. It is the schematic diagram which showed the conventional receiving module.

Explanation of symbols

11 Photodiode 12, 17 Capacitor 13 Resistor 14 Constant voltage source 15, 16 Transimpedance amplifier 45, 46, 47 Differential transimpedance amplifier 51 Transimpedance amplifier 52 Operational amplifier 53, 54 Resistor 55 Capacitor 61 Photodiode 62, 67 Capacitor 63 Resistor 64 Constant Voltage source 65 Transimpedance amplifier 66 Signal speed switching terminal

Claims (4)

A light receiving element that converts the received optical signal into an electrical signal;
In a receiving module comprising an electrical amplifying element that amplifies the converted electrical signal,
The electrical amplifying element, to accommodate both the two optical signals different Do that the signal speed in one of the electric amplifier element, the signal amplification characteristic having a frequency band of the gain and the optical signal suitable for signal speed of the optical signal Bei to give a frequency characteristic obtained by adding a,
The optical signal is a multi-rate signal that is modulated by the NRZ method and transmitted at a signal speed of either 1.25 Gbps or 10.3125 Gbps for each optical signal;
The gain suitable for the signal speed of each optical signal is higher for the signal speed of 1.25 Gbps than the gain for the signal speed of 10.3125 Gbps,
The signal amplification characteristic having the frequency band of each optical signal has a flat gain from at least a frequency of 3 GHz to 8 GHz for the signal speed of 10.3125 Gbps, and at least a frequency for the signal speed of 1.25 Gbps. The gain is flat from 0 GHz to the frequency required to pass a 1.25 Gbps signal modulated by the NRZ system, and
The receiving module is characterized by having a frequency of 1.5 GHz or less .   2. The reception according to claim 1, wherein the electric amplifying element is configured by arranging at least two transimpedance amplifiers having different gains and frequency bands in parallel or in combination of parallel and series. module. The electrical amplification element is configured by at least one transimpedance amplifier, and a feedback circuit in the transimpedance amplifier is configured by combining one or more passive elements and active elements. Receive module. 4. The receiving module according to claim 3, wherein a circuit configuration in which at least two of the electric amplifying elements are arranged in parallel or a combination of parallel and series is formed on one monolithic integrated circuit.

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